1. Field of the Invention
The present invention relates to an improvement in the wet adhesion and blocking resistance of paints based on aqueous polymer dispersions.
2. Description of the Prior Art
The adhesion of paint films based on aqueous polymer dispersions to smooth substrates coated with oil-based or alkyd resin-based paints which have not weathered is frequently unsatisfactory even in the dry state. Furthermore, the adhesion depends on the wetness and in general decreases with increasing wetness of the paint films. In practice, this often results in damage to the paint films and there have therefore been many attempts to improve the wet adhesion of paint films based on aqueous polymer dispersions. For example, an attempt has been made (cf. U.S. Pat. No. 3,356,627) to improve the wet adhesion by the presence of special auxiliary monomers, for example basic acrylates, eg. ureidoacrylates, as copolymerized units in the binder polymers employed. Further attempts to improve the wet adhesion of paint films have been made by copolymerization of auxiliary monomers containing glycidyl groups and subsequent reaction of the glycidyl groups with ammonia, hexamethylenetetramine or lower primary or secondary monoamines (cf. U.S. Pat. Nos. 3,350,339, 4,089,829 and 3,969,296). Finally, it has already been proposed (British Pat. No. 1,527,616) to improve the wet adhesion of paint films containing a binder polymer by introducing copolymerized units of .alpha.,.beta.-unsaturated halogen compounds into the polymers and then reacting them with ammonia or hexamethylenetetramine. The reaction of binder polymers, containing carboxyl groups, with alkyleneimines, especially ethyleneimine and 1,2-propyleneimine, is also alleged (cf. British Pat. No. 1,434,535) to improve the wet adhesion. However, the binder polymer dispersions improved by these conventional methods give paint films whose wet adhesion continues not to be fully satisfactory, and which furthermore often block. In addition, the wet adhesion of paint films prepared with such conventional binder dispersions often depends very greatly on the components, eg. pigments, additionally contained in the paints, and is sometimes difficult to reproduce.